1. Field of the Invention
The present invention relates to an element formation substrate having an SOI (Silicon On Insulator) region and a non-SOI region on the major surface side and a method of manufacturing the same. The present invention also relates to a semiconductor device using the element formation substrate.
2. Description of the Related Art
In recent years, an SOI substrate having an SOI layer formed on an Si substrate is used as an element formation substrate. In addition, various methods (so-called partial SOI technologies) of forming a non-SOI region other than an SOI region on part of an SOI substrate, forming a circuit section compatible with a substrate floating effect in the SOI region, and forming a circuit section incompatible with the substrate floating effect in the non-SOI region have been proposed.
For example, the SOI layer and buried insulating layer (BOX layer) on an SOI substrate are partially removed by etching. A silicon layer is epitaxially grown in the etching region and planarized by polishing, thereby forming a non-SOI region (e.g., Jpn. Pat. Appln. KOKAI Publication No. 8-17694). Alternatively, a bulk region is surrounded by an insulating spacer and conductive spacer to form a non-SOI region whereby the floating body effect is canceled and the SOI region is electrically disconnected from the non-SOI region (e.g., Jpn. Pat. Appln. KOKAI Publication No. 11-17001).
In either method, however, no detailed description is done in association with the structure of the SOI substrate used as a base and the structure of the BOX layer in the SOI region. For example, when an SOI substrate prepared by the bonding method is used as a base, its bonding interface is exposed as a support substrate surface by partially removing the SOI layer and BOX layer. Hence, undesired foreign substances that are inserted in the bonding process may sometimes remain on the support substrate surface. If foreign substances remain on the support substrate surface, it is difficult to form a high-quality non-SOI region. In addition, if the support substrate surface has metal contamination, it is difficult to control its influence on a semiconductor device when a non-SOI region is to be formed, or a semiconductor device is to be formed in the non-SOI region.
As described above, in the conventional element formation substrate prepared by forming a non-SOI region on an SOI substrate, the poor quality of the non-SOI region poses a problem.